result = switch(shape) {
rectangle = function(r)
return "a rectangle with width " .. r.width
end,
function(s)
return "an unknown shape"
end
}
[0]: https://gist.github.com/krajzeg/9bd8806fb72c1ae22eb931b42b3d...
(Implicitly) using [1] instead of [false] as a default is less typing for sure (but maybe a bit more confusing?).
Also, objects being switched on really have to be tables in my version anyway (since overriding __call for builtin types seems harsh to me), so having a tag field right in them as opposed to creating a metatable should be more efficient.
For my version I'll add a value-weak map of metatables to dedup them, should work as well.
In terms of functions, yeah, I don't think you can get rid of them, but (in the example) you can avoid (r) and (s) params if you assume that the functions lexically close over shape.
I admit it takes a minute to grok, and the example of a_square being a rectangle but not a square added some unnecessary confusion.
I found it nice how it's possible to emulate switches in Lua with so little code, without the result looking too ugly. You may find this pattern useful. That's it.
The catch is that, unlike with normal switches or with a series of "if"s, there's a whole bunch of indirection added via functions, so it's not very efficient.
Perhaps LuaJIT can inline these functions, but I haven't tested it.